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/*
KeePass Password Safe - The Open-Source Password Manager
Copyright (C) 2003-2021 Dominik Reichl <dominik.reichl@t-online.de>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.Text;
#if !KeePassUAP
using System.Security.Cryptography;
#endif
using KeePassLib.Utility;
#if !KeePassLibSD
namespace KeePassLib.Cryptography
{
/// <summary>
/// Generate HMAC-based one-time passwords as specified in RFC 4226.
/// </summary>
public static class HmacOtp
{
private static readonly uint[] g_vDigitsPower = new uint[] { 1,
10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000 };
public static string Generate(byte[] pbSecret, ulong uFactor,
uint uCodeDigits, bool bAddChecksum, int iTruncationOffset)
{
return Generate(pbSecret, uFactor, uCodeDigits, bAddChecksum,
iTruncationOffset, string.Empty);
}
internal static string Generate(byte[] pbSecret, ulong uFactor,
uint uCodeDigits, bool bAddChecksum, int iTruncationOffset,
string strAlg)
{
if(pbSecret == null) { Debug.Assert(false); pbSecret = MemUtil.EmptyByteArray; }
if(uCodeDigits == 0) { Debug.Assert(false); return string.Empty; }
if(uCodeDigits > 8) { Debug.Assert(false); uCodeDigits = 8; }
byte[] pbText = MemUtil.UInt64ToBytes(uFactor);
Array.Reverse(pbText); // To big-endian
byte[] pbHash;
if(strAlg == "HMAC-SHA-256")
{
using(HMACSHA256 h = new HMACSHA256(pbSecret))
{
pbHash = h.ComputeHash(pbText);
}
}
else if(strAlg == "HMAC-SHA-512")
{
using(HMACSHA512 h = new HMACSHA512(pbSecret))
{
pbHash = h.ComputeHash(pbText);
}
}
else
{
Debug.Assert(string.IsNullOrEmpty(strAlg) || (strAlg == "HMAC-SHA-1"));
using(HMACSHA1 h = new HMACSHA1(pbSecret))
{
pbHash = h.ComputeHash(pbText);
}
}
uint uOffset = (uint)(pbHash[pbHash.Length - 1] & 0xF);
if((iTruncationOffset >= 0) && (iTruncationOffset < (pbHash.Length - 4)))
uOffset = (uint)iTruncationOffset;
uint uBinary = (uint)(((pbHash[uOffset] & 0x7F) << 24) |
((pbHash[uOffset + 1] & 0xFF) << 16) |
((pbHash[uOffset + 2] & 0xFF) << 8) |
(pbHash[uOffset + 3] & 0xFF));
uint uOtp = (uBinary % g_vDigitsPower[uCodeDigits]);
if(bAddChecksum)
uOtp = ((uOtp * 10) + CalculateChecksum(uOtp, uCodeDigits));
uint uDigits = (bAddChecksum ? (uCodeDigits + 1) : uCodeDigits);
return uOtp.ToString(NumberFormatInfo.InvariantInfo).PadLeft(
(int)uDigits, '0');
}
private static readonly uint[] g_vDoubleDigits = new uint[] {
0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
private static uint CalculateChecksum(uint uNum, uint uDigits)
{
bool bDoubleDigit = true;
uint uTotal = 0;
while(0 < uDigits--)
{
uint uDigit = (uNum % 10);
uNum /= 10;
if(bDoubleDigit) uDigit = g_vDoubleDigits[uDigit];
uTotal += uDigit;
bDoubleDigit = !bDoubleDigit;
}
uint uResult = (uTotal % 10);
if(uResult != 0) uResult = 10 - uResult;
return uResult;
}
// RFC 6238
internal static string GenerateTimeOtp(byte[] pbSecret, DateTime? odt,
uint uTimeStep, uint uCodeDigits, string strAlg)
{
DateTime dt = (odt.HasValue ? TimeUtil.ToUtc(odt.Value, true) :
DateTime.UtcNow);
ulong uStep = ((uTimeStep != 0) ? uTimeStep : 30U);
ulong uTime = (ulong)TimeUtil.SerializeUnix(dt) / uStep;
return Generate(pbSecret, uTime, uCodeDigits, false, -1, strAlg);
}
}
}
#endif
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